Medium for identifying an object and method for making the same

ABSTRACT

In an identification medium for identifying an authenticity of an object either visually or optically by using an identification device, high polymer cholesteric liquid crystal is applied onto the object, onto a sticker adapted to affixed to the object or onto a base for hot stamping onto the object, and the high polymer cholesteric liquid crystal is patterned, and/or a graphic representation layer such as a figure and letter is formed under or over the high polymer cholesteric liquid crystal to enhance the aesthetic quality of the identification medium or the object, and improve the capability to identify and prevent forgery.

[0001] This application claims priority from PCT/JP01/09157, filed Oct.18, 2001, and JP2000-318779, filed Oct. 19, 2000, incorporated herein byreference.

TECHNICAL FIELD

[0002] The present invention relates to a medium and method forpreventing forgery of two-dimensional and three-dimensional objects suchas passports, cards, security notes, gift certificates, pictures, publictransportation tickets, and public betting tickets.

BACKGROUND OF THE INVENTION

[0003] Conventionally, hologram has been used as an identificationmedium for preventing the forgery of cards, security notes and coupons.However, as the fabrication of hologram gets easier over time, forgeryhas become more and more common, and some of the cases of forgery, inparticular those in connection with media for visual identification, areso undistinguishable from authentic ones that it is virtually impossibleto tell them apart. Therefore, there is a need for new identificationmedia.

[0004] Japanese patent laid open publication (kokai) No. 63-51193discloses the use of high polymer cholesteric liquid crystal as anidentification medium, and the light reflected therefrom is detectedeither visually or by using an optical identification device.

[0005] Cholesteric liquid crystal normally has a layered structure, andthe axial directions of the molecules in each layer are parallel to eachother as well to the plane of the layer. Each layer is slightly twistedrelative to the adjacent layer so that a three-dimensional spiralstructure is produced. This structure demonstrates the property toselectively reflect a circularly polarized light having a wavelength ofλ which is given by λ=n·p where p is the depth of the layers for thisaxial direction to turn 360 degrees or the pitch, and n is the averageindex of refraction of each layer. Low polymer cholesteric liquidcrystal is used for thermometers whose color changes with temperaturebecause the pitch p distinctly changes with temperature as well as fordisplay devices.

[0006] On the other hand, high polymer cholesteric liquid crystal isprovided with a relatively fixed crystal structure so that the pitch pchanges very little with temperature, magnetic field and electric field,and selectively reflects light of a certain predetermined color(wavelength). High polymer cholesteric liquid crystal can be prepared,for instance, by heating high polymer having a property to be formedinto thermotropic cholesteric liquid crystal beyond the liquid crystaltransition temperature to cause a liquid crystal structure to grow, andfixing the liquid crystal structure by rapidly cooling it.

[0007] For instance, when high polymer cholesteric liquid crystal thatreflects red light having a prescribed wavelength λ_(R) is placed overmaterial which absorbs visible light such as black paper, and randomlight such as sun light is projected thereon, the transmissive light istotally absorbed by the underlying black paper, and only left circularlypolarized light having the wavelength of λ_(R) is reflected. It producesan attractive special color which may be called as cholesteric color.This light however can be shut off if a filter for blocking leftcircularly polarized light is placed thereon.

[0008] When high polymer cholesteric liquid crystal that reflects redlight having a prescribed wavelength λ_(R) is placed over material whichreflects visible light such as white paper, and random light such as sunlight is projected thereon, the underlying white color becomes visible.If a filter for transmitting only left circularly polarized light isplaced thereon, only the reflected left circularly polarized lighthaving the wavelength of λ_(R) become visible as red light. If leftcircularly polarized light having the wavelength of λ_(R) instead of sunlight is projected thereon, only the reflected light having thewavelength of λ_(R) becomes visible even without using a filter.

[0009] However, when reflected light is used for identification purpose,although the high polymer cholesteric liquid crystal demonstrates aunique cholesteric color, and is attractive in appearance, it cannotprovide a generally agreeable appearance by itself, and has beenconsidered inadequate as an identification medium of an object whoseaesthetic appearance is important. The graphic shapes (graphic shapesand patterns) formed on the identification medium are also an importantfactor in identifying the object. In this regard also, a furtherimprovement of identification media using high polymer cholestericliquid crystal is desired.

BRIEF SUMMARY OF THE INVENTION

[0010] The present invention was made in view of such problems of theprior art, and its primary object is to provide an identification mediumwhich provides an improved identification capability, is highlydifficult to illicitly duplicate, is highly attractive in terms of bothshape and color, and is easy to fabricate, and a method for making suchan identification medium.

[0011] According to the present invention, such an object can beaccomplished by providing an identification medium for identifying anauthenticity of an object either visually or optically by using anidentification device, characterized by that: the identification mediumcomprises high polymer cholesteric liquid crystal which is patterned,and/or a graphic representation layer such as a figure and letter whichunderlies or overlies high polymer cholesteric liquid crystal, and byproviding a method for making an identification medium for identifyingan authenticity of an object either visually or optically by using anidentification device, characterized by the steps of: applying highpolymer cholesteric liquid crystal onto the object, onto a stickeradapted to be affixed to the object or onto a base for hot stamping ontothe object, and patterning the high polymer cholesteric liquid crystal,and/or forming a graphic representation layer such as a figure andletter under or over the high polymer cholesteric liquid crystal.

[0012] This enhances the aesthetic appearance, and improves thecapability to identify the object and prevent an illicit duplication ofthe object.

[0013] In particular, by patterning the high polymer cholesteric liquidcrystal by etching or by using laser, the high polymer cholestericliquid crystal can be accurately and easily patterned into a desiredshape so that its aesthetic appearance and identification capability canbe both improved. By printing on the high polymer cholesteric liquidcrystal, the printed color shows on the printed part and the cholestericcolor shows on the exposed surface of the high polymer cholestericliquid crystal so that the freedom in design is enhanced. By thermallytransferring the high polymer cholesteric liquid crystal according to aprescribed pattern, small batch production is facilitated. By partlymodifying the high polymer cholesteric liquid crystal by laser, the highpolymer cholesteric liquid crystal is provided with partly differentoptical properties, and its aesthetic appearance and identificationcapability can be both improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Now the present invention is described in the following withreference to the appended drawings, in which:

[0015]FIG. 1 is a plan view showing an identification medium given as afirst embodiment of the present invention:

[0016]FIG. 2 is a diagram showing the manufacturing process of theidentification medium of the first embodiment of the present invention;

[0017]FIG. 3 is a plan view showing an identification medium given as asecond embodiment of the present invention;

[0018]FIG. 4 is a diagram showing the manufacturing process of theidentification medium of the second embodiment of the present invention;

[0019]FIG. 5 is a plan view showing an identification medium given as athird embodiment of the present invention;

[0020]FIG. 6 is a plan view showing an identification medium given as afourth embodiment of the present invention;

[0021]FIG. 7a is a diagram showing a device for manufacturing theidentification medium of the fourth embodiment of the present invention;

[0022]FIG. 7b is a ribbon used in the manufacturing device;

[0023]FIG. 8 is a diagram showing the manufacturing process of anidentification medium of a fifth embodiment of the present invention;

[0024]FIG. 9 is a diagram illustrating the manner by which theidentification medium of the first embodiment is identified visually byusing a right and left circularly polarizing filter;

[0025]FIG. 10 is a diagram illustrating the manner by which theidentification medium of the first embodiment is identified visually byusing a right and left circularly polarizing filter;

[0026]FIG. 11 is a diagram illustrating the manner by which theidentification medium of the second embodiment is identified visually byusing a right and left circularly polarizing filter;

[0027]FIG. 12 is a diagram illustrating the manner by which theidentification medium of the third embodiment is identified visually byusing a right and left circularly polarizing filter;

[0028]FIG. 13 is a diagram illustrating the manner by which theidentification medium of the fourth embodiment is identified visually byusing a right and left circularly polarizing filter;

[0029]FIG. 14 is a diagram illustrating the manner by which theidentification medium of the fourth embodiment is identified visually byusing a right and left circularly polarizing filter;

[0030]FIG. 15 is a diagram showing the structure of a device formechanically identifying an identification medium according to thepresent invention;

[0031]FIG. 16 is a graph showing the output of a light receiving unit ofthe identification device of FIG. 15;

[0032]FIG. 17a is a front view showing an actual exemplary layout andstructure of the identification device of FIG. 15;

[0033]FIG. 17b is a sectional side view taken along line XVII-XVII ofFIG. 17a;

[0034]FIG. 18a is a front view showing another actual exemplary layoutand structure of the identification device of FIG. 15; and

[0035]FIG. 18b is a sectional side view taken along line XVII-XVII ofFIG. 18a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Preferred embodiments of the present invention are described inthe following.

[0037]FIG. 1 is a plan view showing a first embodiment of the presentinvention including an identification medium 1 which is affixedgenerally to an object X or to a prescribed location thereof andconsists of a single part or two or more parts, the object consisting ofa card, passport, security note, gift certificate or the like. Referringto FIG. 2, the identification medium 1 is formed as a sticker by (a)coating high polymer cholesteric liquid crystal 4 over a base film 3,(b) applying a layer of resist 5 over the assembly, (c) photographicallyexposing the resist 5 by using a mask having a prescribed pattern asshown in FIG. 1 and curing the resist, (d) etching away the part of theresist which has not cured and the high polymer cholesteric liquidcrystal under it by using acid or alkaline chemicals such as nitricacid, hydrochloric acid and ammonium fluoride, (e) removing theremaining resist, and (f) generally applying a coating of a bondingagent or adhesive agent 6. The etching may also consist of dry etchingusing carbon tetrafluoride, for instance, instead of the wet etchingusing the above mentioned chemicals.

[0038] The identification medium 1 in the form of a sticker is used withthe base film 3 facing outward, and is affixed to the object X via thebonding agent or adhesive agent 6.

[0039] The bonding agent or adhesive agent 6 has such a high mechanicalstrength that any attempt to peel off the sticker from the object X willresult in the destruction of the high polymer cholesteric liquid crystal4, thereby preventing the reuse of the sticker.

[0040] In practice, the identification medium may also be formeddirectly on the surface of the object X by the steps of (a) to (e). Ifhigh polymer cholesteric liquid crystal 4 is applied to a base film 3via a peel layer, and a hot melt layer is applied thereon following anetching process, the assembly can be used as a medium for hot stampingwhich is suitable for mass production. Hot stamping consists of aprocess by which an ornamental film is transferred onto the surface ofan object by using instantaneous heat and pressure.

[0041] By etching the high polymer cholesteric liquid crystal 4, highlyfine patterns and letters can be formed at will. This contributes to theenhancement of aesthetic quality and the protection of forgery.

[0042]FIG. 3 is a plan view showing a second embodiment of the presentinvention including identification medium 11 which is affixed generallyto the surface of an object X or to a prescribed location thereof andconsists of one or a plurality of parts. As shown in FIG. 4, theidentification medium 11 is prepared in the form of a sticker by (a)coating high polymer cholesteric liquid crystal 14 over a base film 13,(b) printing a layer of ink 15 thereon according to a prescribed patternas illustrated in FIG. 3, and (c) generally applying a coating of abonding agent or adhesive agent 16. In this embodiment also, theidentification medium may be directly formed on the surface of theobject X or may be formed as a medium for hot stamping.

[0043] In this embodiment also, the high polymer cholesteric liquidcrystal 14 and ink layer 15 may be directly formed on the object X,instead of on the base film 13, as was the case with the firstembodiment, and the assembly may also be used as a medium for hotstamping.

[0044]FIG. 5 is a plan view showing a third embodiment of the presentinvention including an identification medium 21 which is affixedgenerally to the surface of an object X or to a prescribed locationthereof, and consists of one or a plurality of parts. In thisidentification medium assembly, a layer of high polymer cholestericliquid crystal 24 is formed into a desired shape as was done in thefirst embodiment, and a desired printing process is performed as wasdone in the second embodiment. Numeral 21 a denotes a part which hasbeen etched away, and numeral 21 b denotes a part which is printed.

[0045]FIG. 6 is a plan view showing a third embodiment of the presentinvention including an identification medium 31 which is affixedgenerally to the surface of an object X or to a prescribed locationthereof. This identification medium 31 is a combination of three partsof high polymer cholesteric liquid crystal 34 a, 34 b and 34 c havingthree different kinds of reflective wavelength selectivity and/orcircularly polarizing reflective property of a specific direction (rightor left). For instance, the medium may include three parts of highpolymer cholesteric liquid crystal that reflect right circularlypolarized light of three different colors, blue color for the letters 34a, red color for the central star-shaped region 34 b and green color forthe outer star-shaped region 34 c. Therefore, if the surface of theobject X is black in color, for instance, the patterns and letters inthe three colors can be visually seen. The colors also change dependingon the color of the surface of the object X and the color of the bondingagent. When a circularly polarizing filter is used as will be describedhereinafter, an even more accurate determination of authenticity becomespossible.

[0046] The identification medium 31 is formed by transferring the threeparts of high polymer cholesteric liquid crystal 34 a, 34 b and 34 chaving different properties supported by a ribbon onto the object X at aprescribed pattern as shown in FIG. 7a. More specifically, as shown inFIG. 7b, the ribbon 37 is formed by placing three parts of high polymercholesteric liquid crystal on a base film 33 one next to the other,coating a bonding agent 36, and winding the assembly into a roll. Heatis applied to the ribbon by using a thermal head 38 of a thermal printerat a prescribed timing while the ribbon 37 is moved relative to theobject X in the same way as in a known thermal printer. Thereby, desiredparts of the high polymer cholesteric liquid crystal are peeled off fromthe base film 33, and are transferred upon the object X at theprescribed pattern.

[0047] The process of transferring the corresponding parts of the highpolymer cholesteric liquid crystal does not require a metallic die setor a master plate, and allows letters and shapes to be formed at will.In particular, a substantial saving in cost can be achieved when theproduction batches are small in quantity. By increasing the number ofkinds of the high polymer cholesteric liquid crystal that are used, thenumber of available colors increases.

[0048] Furthermore, as shown in FIG. 8, letters and patterns 45 can alsobe drawn by scorching and discoloring selected parts of the high polymercholesteric liquid crystal 44 by using a laser device 40. If the powerof the laser is controlled, and the scorching process is conducted in agradual manner, it is possible to change the pitch p (the distancerequired for each layer to twist by one turn) and change the color ofthe reflected light. Therefore, letters and patterns can be formed bythe parts which are subjected to the laser and have thereby been made toreflect light of different colors.

[0049] In the first embodiment, if the high polymer cholesteric liquidcrystal 4 of the identification medium 1 reflects only red rightcircularly polarized light and the bonding agent 6 is transparent whilethe surface of the object X is black or the bonding agent is black, theview obtained by a simple identification device 51 consisting of a leftcircularly polarizing filter 51 a and a right circularly polarizingfilter 51 b placed one next to the other will be as given in FIG. 9.More specifically, the right circularly polarizing filter 51 b allowsthe image formed by the high polymer cholesteric liquid crystal 4 of theidentification medium 1 that reflects only right circularly polarizedlight or the graphic pattern of the identification medium 1 to betransmitted or viewed. On the other hand, the left circularly polarizingfilter 51 a shuts off the graphic pattern of the identification medium 1from view, and allows only the surface of the object X or the blackbackground of the bonding agent 6 to be viewed. If the bonding agent 6is transparent and a pattern is formed on the surface of the object X,the identification medium 1 appears semi-transparent, and the surfacepattern and graphic pattern of the identification medium show dimly tothe naked eye. However, the simple identification device 51 allows onlythe surface pattern to be viewed as shown in FIG. 10 because the leftcircularly polarizing filter 51 a shuts off the graphic pattern of theidentification medium 1.

[0050] In the second embodiment, if the high polymer cholesteric liquidcrystal 14 of the identification medium 11 reflects only red rightcircularly polarized light, the view obtained by the simpleidentification device 51 will be as given in FIG. 11. More specifically,the right circularizing filter 51 b transmits only the light reflectedby the high polymer cholesteric liquid crystal 14 thereby making the ink15 or printed image underlying the high polymer cholesteric liquidcrystal 14 invisible while the left circularly polarizing filter 51 ashuts off the light reflected by the high polymer cholesteric liquidcrystal 14 thereby making only the printed image or the ink 15underlying the high polymer cholesteric liquid crystal 14 visible.

[0051] In the third embodiment, if the high polymer cholesteric liquidcrystal 24 of the identification medium 21 reflects only red rightcircularly polarized light, the view obtained by the simpleidentification device 51 will be as given in FIG. 12. More specifically,the right circularizing filter 51 b makes only the image etched out ofthe high polymer cholesteric liquid crystal 24 visible while the leftcircularly polarizing filter 51 a shuts off the light reflected by thehigh polymer cholesteric liquid crystal 24 thereby making only theprinted letters 21 b visible.

[0052] In the fourth embodiment, if the three parts of the high polymercholesteric liquid crystal 34 a, 34 b and 34 c of the identificationmedium 31 reflect only right circularly polarized light of differentcolors, and the bonding agent (not shown in the drawing) is transparentwhile the surface of the object X is black or the bonding agent isblack, the view obtained by a simple identification device 51 will be asshown in FIG. 13 when the bonding agent is black and as shown in FIG. 14when the bonding agent is transparent. The pattern appears in the sameway as the first embodiment illustrated in FIGS. 9 and 10, and only thecolors are different.

[0053] The device for mechanically identifying the identification mediumsuch as those given in the first to fifth embodiments is described inthe following. Referring to FIG. 15, the identification device 61consists of a pair identification units 61 a and 61 b. Theidentification unit 61 a comprises a light source 62, a light receivingunit 63 and a right circularly polarizing filter 64 so that rightcircularly polarized light is impinged upon the object X and only rightcircularly polarized light is transmitted to the light receiving unit 63while left circularly polarized light is shut off. The identificationunit 61 b comprises a light source 65, a light receiving unit 66 and aleft circularly polarizing filter 67 so that left circularly polarizedlight is impinged upon the object X and only left circularly polarizedlight is transmitted to the light receiving unit 66 while rightcircularlypolarized light is shut off. The light sources 62 and 65preferably consist of light bulbs, LEDs or laser sources, but are notlimited to them.

[0054] The light receiving outputs from the light receiving units 63 and66 of these identification units are given in FIGS. 16 for the cases ofan identification medium consisting of high polymer cholesteric liquidcrystal, a metallic vapor deposition layer tinted so as to have theappearance of high polymer cholesteric liquid crystal, and a combinationof such a metallic vapor deposition layer and a film producing a phasedelay of one-half the wavelength.

[0055] In the case of high polymer cholesteric liquid crystal, the lightreceiving unit 63 of the identification unit 61 a produces an outputbecause the right circularly polarized light reflected by the highpolymer cholesteric liquid crystal transmits through the rightcircularly polarizing filter 64 while the light receiving unit 66 of theidentification unit 61 b does not produce an output because leftcircularly polarized light is impinged upon the high polymer cholestericliquid crystal, and no light is reflected therefrom.

[0056] In the case of a metallic vapor deposition layer, there is nosubstantial output from the light receiving unit 63 because rightcircularly polarized light is reversed by the metallic vapor depositionlayer in the identification unit 61 a and converted into left circularlypolarized light which is in turn shut off by the right circularlypolarizing filter 64. There is also no substantial output from the lightreceiving unit 66.

[0057] When a phase delay film is placed over the metallic vapordeposition layer, an output is obtained from the light receiving unit 63because right circularly polarized light is not reversed by the metallicvapor deposition layer in the identification unit 61 a and reflected asright circularly polarized light which in turn transmits through theright circularly polarizing filter 64. Similarly, an output is obtainedfrom the light receiving unit 66.

[0058] Thus, when high polymer cholesteric liquid crystal is used, whena metallic vapor deposition layer is used, and when a combination of ametallic vapor deposition layer and a half-wavelength phase delay filmis used, different kinds of output are obtained. The presence of highpolymer cholesteric liquid crystal can be determined depending on if thereceived light output ratio (output from the light receiving unit66/output from the light receiving unit 63) is substantially zero ornot. The authenticity can be therefore easily and accurately determinedfrom the pattern (figures and patterns).

[0059]FIGS. 17a and 17 b show a possible actual structure of theidentification device 61. FIGS. 18a and 18 b show another possibleactual structure of the identification device 61. The identificationdevice 61 shown in FIGS. 17a and 17 b includes the identification unit61 a and identification unit 61 b which are arranged parallel to eachother so as to identify two different points of an identification mediumhaving a certain width, independently from each other. Theidentification device 61 shown in FIGS. 18a and 18 b includes theidentification unit 61 a and identification unit 61 b which are arrangedin a mutually crossing relationship so as to impinge light upon a samepoint and simultaneously identify a same point of the identificationmedium. The latter case allows the size of the identification object tobe minimized, and the identification reliability to be improved.

[0060] The identification media described above may be formed on variouscards, gift certificates and photographs of IDs and passports, and mayalso be formed into paper in the form of tape such as thread hologram.

[0061] Although the present invention has been described in terms ofpreferred embodiments thereof, it is obvious to a person skilled in theart that various alterations and modifications are possible withoutdeparting from the scope of the present invention which is set forth inthe appended claims.

1. An identification medium for identifying an authenticity of an objecteither visually or optically by using an identification device,characterized by that: the identification medium comprises high polymercholesteric liquid crystal which is patterned and/or a graphicrepresentation layer such as a figure and letter which underlies oroverlies high polymer cholesteric liquid crystal.
 2. An identificationmedium according to claim 1, wherein the identification medium compriseshigh polymer cholesteric liquid crystal which is patterned by etching.3. An identification medium according to claim 1, wherein theidentification medium comprises a printed layer underlying the highpolymer cholesteric liquid crystal
 4. An identification medium accordingto claim 1, wherein the identification medium comprises high polymercholesteric liquid crystal which is thermally transferred according to aprescribed pattern.
 5. An identification medium according to claim 1,wherein the identification medium comprises high polymer cholestericliquid crystal which is partly modified by laser according to aprescribed pattern.
 6. A method for making an identification medium foridentifying an authenticity of an object either visually or optically byusing an identification device, characterized by the steps of: applyinghigh polymer cholesteric liquid crystal onto the object, onto a stickeradapted to be affixed to the object or onto a base for hot stamping ontothe object; and patterning the high polymer cholesteric liquid crystal,and/or forming a graphic representation layer such as a figure andletter under or over the high polymer cholesteric liquid crystal.
 7. Amethod for making an identification medium according to claim 6, whereinthe high polymer cholesteric liquid crystal is patterned by etching. 8.A method for making an identification medium according to claim 6,wherein an ink layer underlying the high polymer cholesteric liquidcrystal is formed by printing.
 9. A method for making an identificationmedium according to claim 6, wherein the high polymer cholesteric liquidcrystal is thermally transferred onto the object, onto a sticker adaptedto affixed to the object or onto a base for hot stamping onto the objectaccording to a prescribed pattern.
 10. A method for making anidentification medium according to claim 6, wherein the high polymercholesteric liquid crystal is partly modified by laser according to aprescribed pattern.